The present disclosure relates to a vibration generating apparatus.
A vibration generating apparatus, converting electrical energy into mechanical vibrations using the principle of the generation of electromagnetic force, has been commonly been mounted in mobile phones, or the like, to be used for silently notifying a user of call reception by transferring vibrations thereto.
In addition, in accordance with the rapid expansion in the market for mobile devices such as mobile phones, and the like, mobile devices have been widely been implemented with increased functionality. In addition, the miniaturization of mobile devices has been demanded, along with improvements in the quality thereof.
In accordance with this trend, demand for development of a vibration generating apparatus having a novel structure capable of overcoming disadvantages of an existing vibration generating apparatus and significantly improving quality has increased.
Further, recently, mobile phones have largely been replaced by smartphones, and a touchscreen scheme has been adopted in the smart phone. Therefore, the use of a vibration generating apparatus has increased for the purpose of generating vibrations for user feedback at the time of a touch.
In addition, recently, a vibration generating apparatus using a piezoelectric element has been released onto the market. The vibration generating apparatus, which uses the principle of an inverse piezoelectric effect in generating displacement by applying voltage to the piezoelectric element, allows a mass body of a mover to move by the generated displacement to generate vibrational force.
In the vibration generating apparatus having the above-mentioned structure, a bandwidth of a frequency at which vibration force of a predetermined level or more may be obtained is wide, such that stable vibration characteristics may be implemented.
Meanwhile, the piezoelectric element is installed on a vibration member. Here, the piezoelectric element is bonded to the vibration member through a thermosetting adhesive. That is, the piezoelectric element and the vibration member are attached to each other through the thermosetting adhesive having relative high coupling force in order to prevent separation between the piezoelectric element and the vibration member. In addition, the thermosetting adhesive has a feature of being hardenable at high temperature.
Heat is applied in order to harden the thermosetting adhesive for attaching the piezoelectric element and the vibration member to each other. However, in this case, there may be a problem in that the vibration member may be deformed and bent due to a difference in a coefficient of thermal expansion between the piezoelectric element and the vibration member.
In order to solve this problem, the vibration member may be formed of a material having a low coefficient of thermal expansion (for example, a material containing 36 wt % or more of nickel). However, the vibration member is formed of the material having the low coefficient of thermal expansion as described above, such that the vibration member may be damaged at the time of vibrations.
Therefore, the development of a structure capable of preventing damage to the vibration member while maintaining coupling force between the piezoelectric element and the vibration member has been urgently demanded.